1. Field of the Invention
The present invention relates to a combustion engine waste heat recovering apparatus and particularly to a heat recovering apparatus for recovering heat generated by an engine used as a power source in cogeneration system.
2. Description of the Related Art
As the need for global environmental protection has been focused, cogeneration system are widely proposed for electric power generation and hot water supply with the use of a gas engine as the power source which consumes city gas as a fuel. Such a type of cogeneration systems are favorably used in cold districts in view of the effectiveness in the use of heat. However, as the viscosity of an engine oil in the gas engine becomes high in winters or every chilly morning and night when the air temperature is low, a large torque is needed for starting the engine.
Also, although depending on the condition of a mixture of fuel and air, water in the non-combusted mixture gas or the remaining exhaust gas may condenses into small droplets in low temperatures thus disturbing the ignition of an ignition plug.
It is known that the above drawback can simply be eliminated by use of an electric heater for warming up the engine. However, if there is only a limited room about the engine for mounting the electric heater, a sufficiently powerful type of the electric heater can hardly be installed. Even when there is a room for a bulky type of the electric heater with sufficient power, the consumption of electric power of the electric heater is considerably high and may be uneconomical.
It is an object of the present invention to provide an engine waste heat recovering apparatus capable of warming up the engine with the action of a heat recovery pump without using such a bulky component as an electric heater requiring a sizable space for installation.
As a first feature of the present invention, an engine waste heat recovering apparatus which circulates a thermal medium through a heat recovery section of the engine to recover exhaust heat from the engine, comprising: a conduit for circulating the thermal medium across a heat exchanger in an external hot water storage tank, a pump mounted across the conduit, a means for measuring the temperature of the engine, and a controller for switching on the pump before starting the engine when the temperature of the engine at the start up is lower than a reference temperature predetermined for permitting the engine to be started.
As a second feature of the present invention, the heat recovery section of the engine includes an engine cooling unit equipped with a water jacket and an oil heat exchanger for recovering heat from the engine oil, and the circulation path is routed so that the thermal medium runs from the oil heater exchanger to the engine cooling unit.
As a third feature of the present invention, further comprising an exhaust gas heat exchanger for use of exhaust gas from the engine which is mounted across the circulation path at the upstream side of the engine cooling unit and wherein the thermal medium to be conveyed into the exhaust gas heat exchanger is controlled to be at a low temperature so that vapor contained in the exhaust gas of which heat is transferred to the thermal medium, drops down to below its dew point.
As a fourth feature of the present invention, the pump is mounted on the thermal medium inlet side of the oil heat exchanger.
According to the first to fourth features of the present invention, when the temperature of the engine is lower than the reference temperature at the start up of it, the pump is switched on before starting up the engine. This allows the thermal medium kept at a lower temperature by the outer ambient thermal condition in a cold district or in the early morning to be heated by the hot water stored in the separately equipped hot water storage tank through the action of heat exchange. The thermal medium is then conveyed to the heat recovery section of the engine for warming up the engine.
According to the second feature of the present invention, the thermal medium is first conveyed into the oil tank where the oil heat exchanger is installed, hence effectively warming the oil of which the viscosity is high at a lower temperature and readily decreasing the viscosity. After the engine is started and operated in the normal driving mode, the engine oil heated up through the operation of the engine can be efficiently cooled down by the thermal medium.
According to the third feature of the present invention, the temperature of the thermal medium conveyed into the exhaust gas heat exchanger is controlled so that water vapor contained in the exhaust gas drops down to below its dew point. This permits the thermal medium to recover heat from the exhaust gas as well as condensation heat and then be transferred to the engine cooling unit at the downstream of the circulation path where its temperature is increased higher. The thermal medium is further conveyed to the output heat exchanger where its abundantly recovered thermal energy is released.
According to the fourth feature of the present invention, the thermal medium is passed through the pump before recovering heat from the engine. This allows the pump to stay at a relatively low temperature thus minimizing the degradation with time of packings and other sealants.